In a former life (before I started railroading). I worked for a company that installed wind turbine farms. I was the high voltage electrician. Those AC motors/generators worked like this.

Existing power at 60Hz from the power lines were let in to the motor/generator.

The motor/generator would spin at 1800 RPMs.
The wind turbine through a transmission would speed up the shaft speed to 1850 RPMs.
The increase in shaft speed would increase the frequency of the power in the motor/generator and would instead of taking in power, would output power. (So the outcome would be power at 61 Hz. In the power grid, the concern for most of the transmission and distribution engineers was frequency instead of voltage. We would use voltage regulators and frequency converters to take the power produced back to 600VAC@60hz.)

Those were asynchronous motor/generators; meaning no slip rings.

I would imagine that AC dynamic braking would do something like that.

Brian

However, the design could also use synchronous motors, where they may power to rotor with the slip rings and therefor create the dynamic braking.

I am not 100% on this, now a days I am a signal maintainer.